Arctic Oscillation

(abbrev. AO)- The Arctic Oscillation is a pattern in which atmospheric pressure at polar and middle latitudes fluctuates between negative and positive phases. The negative phase brings higher-than-normal pressure over the polar region and lower-than-normal pressure at about 45 degrees north latitude. The negative phase allows cold air to plunge into the Midwestern United States and western Europe, and storms bring rain to the Mediterranean. The positive phase brings the opposite conditions, steering ocean storms farther north and bringing wetter weather to Alaska, Scotland and Scandinavia and drier conditions to areas such as California, Spain and the Middle East. In recent years research has shown, the Arctic Oscillation has been mostly in its positive phase. Some researchers argue that the North Atlantic Oscillation is in fact part of the AO.

An atmospheric circulation pattern in which the atmospheric pressure over the polar regions varies in opposition with that over middle latitudes (about 45 degrees North) on time scales ranging from weeks to decades. The oscillation extends through the depth of the troposphere. During the months of January through March it extends upward into the stratosphere where it modulates in the strength of the westerly vortex that encircles the Arctic polar cap region. The North Atlantic Oscillation and Arctic Oscillation are different ways of describing the same phenomenon.

For more information, see The Arctic Oscillation as an arctic weather pattern.